Implant consisting of bone material

ABSTRACT

The invention relates to a vertebral column implant for intercorporal fusion on the vertebral column, consisting of a body which consists of bone material and which is curved in the direction in which it extends longitudinally. The size of the implant is adapted to the intermediate vertebral space available between adjacent vertebrae after the intermediate vertebral body has been removed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of PCT/EP00/10672 filed Oct.30, 2002, which in turn claims priority of German Patent Application DE199 52 939.6 filed Nov. 3, 1999, the contents of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to an implant for the connection of bonesand in particular to a spinal column implant for the intercorporalfusion of vertebrae which is inserted between two vertebrae to be fused.

BACKGROUND OF THE INVENTION

Through the degeneration of the vertebral disc, in particular of thevertebral disc nucleus (nucleus pulposus) a loss of height in theaffected vertebral disc space often comes about which is connected witha loosening of the vertebral disc annulus (annulus fibrosus) and of theligaments. Through this, the spinal column becomes instable at thislocation. The result is a horizontal displaceability of the vertebralbodies relative to one another (spondylolisthesis), which leads toimpairments of the nerve roots in this region and/or of the spinal cordtogether with the pain resulting from this. Similar symptoms can ariseafter a chemo-enzymatic or physical (laser) disintegration of thevertebral disc nucleus (nucleolysis) for the treatment of a herniateddisc (post-nucleolysis syndrome).

The principle for treating these symptoms consists in the surgicalremoval of the vertebral disc nucleus and the laying in or insertionrespectively of one—in the region of the cervical vertebral column—or oftwo—in the region of the lumbar vertebral column—sufficiently stablebodies in order to restore the normal height of the vertebral discspace.

At the same time the horizontal displaceability must be prevented. Thistakes place either through the implant itself or through additionalmetal implants (instrumented fusion). These implants are subject inparticular in the lumbar vertebral column to considerable forces, whichcan lead to the breakage of the metal implant. Therefore an attempt ismade to have the intermediate vertebral insert grow together or fuserespectively as rapidly and as solidly as possible with the adjacentvertebral bodies.

Essentially two techniques are used for the treatment of patients withspinal trauma or degenerative disease of the spinal column.

-   -   1. Removal of the vertebral disc nucleus and of the cartilage at        the end-plates, expansion of the intervertebral space to a        normal width and insertion of a plano-parallel or horizontally        slightly wedge-shaped block (Smith-Robinson technique).    -   2. Expansion of the vertebral disc space to normal height,        drilling of a cylindrical opening which covers both vertebrae        and insertion of a cylindrical dowel (Cloward technique). The        dowel can in this connection either be a smooth cylinder or have        the shape of a machine bolt.

A relatively new method for the intercorporal fusion at the lumbervertebral column is the posterior lumbar intercorporal fusion in aunilateral transforaminal technique. In this connection, the foramenintervertebrale of the affected segment is opened unilaterally, thevertebral disc space is removed and, for the ventral support, twotitanium lattice baskets are introduced which are cut to the matchingheight and which are filled with bone chips. This tissue-saving methoddoes, however, have different disadvantages. On the one hand, the sharpedges of the titanium baskets can damage the nerve roots duringintroduction. Furthermore, no lordosiation is possible as the basketsare practically introduced blind. Finally, only the rims of the basketare available to absorb the pressure present. The titanium makes thefusion control more difficult due to artifacts and in computertomography. Furthermore, the implant removal in revision operations isextremely difficult.

The object of the present invention therefore lies in providing animplant for the fusion of bones which eliminates the aforesaiddisadvantages.

SUMMARY OF THE INVENTION

This object is satisfied by a spinal column implant for intercorporalfusion at the spinal column consisting of a body of bone material whichhas a substantially rectangular or trapezoidal cross-section and whichis made curved in the direction of its longitudinal extent, whereby oneconvexly curved side and one concavely curved side is formed, andwherein the implant is matched in size to the intervertebral spacebetween adjacent vertebrae after the removal of the intervertebral body.

A special advantage of the spinal column implant in accordance with theinvention is given by the material used which does not represent aforeign body due to its biological origin and to a special preservation.Furthermore, due to the curved design of the implant, the advantageresults that it is matched to the shape of the front edge of the lumbarvertebrae and thus automatically comes into the right position oninsertion.

Further advantageous embodiments of the spinal column implant inaccordance with the present invention are specified in the description,the drawing and the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in the following in a purelyexemplary manner with reference to embodiments of a spinal columnimplant in accordance with the invention and with reference to theaccompanying drawings. There are shown:

FIG. 1 is a plan view of an embodiment of a spinal column implant inaccordance with the present invention;

FIGS. 2 and 3 are in each case possible cross-sectional shapes of thespinal column implants in accordance with the invention;

FIG. 4 is a plan view of a further embodiment of a spinal column implantin accordance with the present invention; and

FIG. 5 is a plan view of a further embodiment of a spinal column implantin accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, the body can consist of processed,preserved and sterile bone material of human origin, a so-calledallograft, or of processed, preserved and sterile bone material ofanimal origin, a so-called xenograft. The body can be made of solidcortical bone material or also of spongeous bone material, for exampleof the humerus, femur, tibia or of other bones either of deceased humansor of animals, in particular of bovine bone material, or also as ahollow body which is then filled with spongeous bone material.

In a particularly advantageous embodiment of the spinal column implantin accordance with the invention, the body has a banana-like curvatureand rounded edges. Such a design of the body facilitates the applicationof the spinal column implant between the vertebral bodies to be fused inthat the roundings avoid a canting of the implant during application.The implant is matched particularly well to the natural shape of the endplates of the vertebral bodies by the special banana shape and so offersthe largest possible contact surface for the end plates. In this way, amore physiological distribution of the forces takes place, wherebypressure peaks and a subsiding of the implant into the vertebral bodiesdue to this are avoided. Since a correct positioning takes placeautomatically due to the curvature of the implant, the restoration ofthe physiological curvature of the spinal column—lordosis—is alsopossible by a trapezoidal cross-section.

It is particularly advantageous when notches or recesses are provided atthe body which make possible the taking along of loosely introduced bonepowder into the intervertebral space. In this way, bone powder canautomatically be introduced into the concavely shaped region of theimplant during insertion of the implant into the intervertebral space.

In accordance with a further aspect of the present invention, receptionopenings are designed at one or more sides of the body as drillings witha thread of a depth of preferably 3 mm. Application tools provided witha matching thread can then be screwed into these tapped drillings inorder to insert the implant in an accurate position between thevertebrae to be fused.

As the material for the spinal column implant in accordance with thepresent invention, a suitable allogenic or xenogenic bone material isprocessed in such a manner that it is preserved, is capable of storage,is sterile and can be used in accordance with its purpose. Thepreservation of the bone material can for example take place by means offreeze drying. Another preferred method for the production of the bonematerial is a processing through preferably solvent dehydration ofnative bone material by means of an organic solvent which is misciblewith water, e.g. methanol, ethanol, propanol, isopropanol, acetone,methyl ethyl ketone or mixtures of these solvents. The preservation andsterilization of the bone material in accordance with this method isalso a subject matter of the patent DE 29 06 650, the contents of whichare taken up into the disclosure of the present application through thisreference.

This method serves for the production of transplant preserves andenables a dehydration and exposure right into the fine structure of thefibrils of the bone material, so that the processed bone material has amorphological structure in a histological view which is very similar tothat of the natural bone, and thus the desired properties of the bonematerial are retained. This method of solvent dehydration also has theadvantage that a substantially lower apparatus cost and complexity isrequired in comparison with freeze drying.

Furthermore, the bone material can also be produced through solventdehydration of bone material with subsequent terminal sterilization, inparticular through irradiation with gamma rays. Alternatively, thespongeous bone material can be produced through aseptic processing ofbone material without terminal sterilization. The starting material ofthe bone implant in accordance with the invention is human or animalbone of sufficient size.

To remove the antigenicity, the bone is subjected to an osmotictreatment. Furthermore, an oxidizing treatment is carried out fordenaturation of soluble proteins. To optimize virus deactivation, areduction of pH to pH 3, or a treatment with caustic soda or anothersubstance which destroys DNA/RNA, can take place. The dehydration takesplace through organic solvents, preferably acetone. The concludingsterilization takes place through high-energy radiation, preferably γrays with a maximum dose of 25 kGy.

A bone treated in this manner maintains its natural mineral collagenbond and properties. Furthermore, a bone treated in this manner can bereworked.

In the figures the same reference symbols designate in each case thesame components of the illustrated embodiments.

The embodiment of a spinal column implant in accordance with theinvention illustrated in FIG. 1 comprises a body 10, which consists, forexample, of cortical, diaphyseal bone material, e.g. of human origin.This body 10 is, in a plan view, substantially elongate and made curvedin the direction of its longitudinal extent.

The two opposite ends 12 and 14 of the body 10 are made rounded suchthat overall a banana-like or also kidney-like design of the base body10 results. The body 10 has a convexly curved surface 16 and a concavelycurved surface 18 between the two ends 12 and 14.

As FIG. 1 shows, the base body has two reception openings 20, 22 forapplication tools in the regions of its one end 12. The receptionopenings 20, 22 are made as drillings whose longitudinal axes do notextend parallel to one another.

In the region of the oppositely disposed end 14, a structured design ofthe surface of the base body is provided in the region of the concavesurface 18, preferably by notches or recesses 24 which allow the takingalong of loosely added bone powder into the intervertebral space. Thetaking along and compacting of the bone powder during the insertion ofthe bone implant into the intervertebral space is ensured by thestructured design of the surface provided (three notches are provided inthe example shown).

FIGS. 2 and 3 show possible cross-sectional shapes of the body 10 alongthe intersection line A-B of FIG. 1.

FIG. 2 shows a possible cross-sectional shape in the form of a rectanglewith rounded edges. FIG. 3 shows a trapezoidal cross-sectional shape,with the obliquely extending sides of the trapezoid deviating from therectangular shape by an angle a of approximately 3° to 6°.

As in particular FIG. 3 shows, with a trapezoidal cross-section of theimplant, the obliquely extending outer sides 17, 19 can be inclined inthe direction of the convex outer surface 18, i.e. in the direction ofthe ring center of the implant formed in the shape of a ring segment.

FIG. 1 shows a substantially symmetrical embodiment of a spinal columnimplant. In contrast to this, an asymmetrical shape is selected in thefurther embodiment shown in FIG. 4, in which the shape of the body 10′in a plan view tapers from the one end 12 in the direction of the otherend 14. In other respects, the same reference numerals designate thesame elements. At the same time, the cross-sectional shapes shown inFIGS. 2 and 3 can also be used in the embodiment shown in FIG. 4.

As FIGS. 1 and 4 show, the bodies 10, 10′ have the form of a ringsegment, with preferably the shape of an approximately ⅜ to ½ ring beingselected. Furthermore, it can be recognized in the embodiment of FIG. 4that the one end 12 of the body 10′ is wider than the oppositelydisposed end 14 in order to facilitate an insertion of the implant intothe foramen intervertebrale.

Generally, the body 1 of the spinal column implant is matched in size tothe pre-determined space at which the implant should be inserted. Theouter dimensions of such a spinal column implant can, for example, be asfollows for a lumbar application: length approximately 30 to 60 mm,width approximately 8 to 20 mm, height approximately 6 to 18 mm.

Generally, the possibility exists of forming the spinal column implantas a solid implant, for example of cortical or of spongeous bone. Analternative embodiment of the invention provides that the spinal columnimplant—likewise made of cortical or spongeous bone—is designed as ahollow body.

FIG. 5 shows such an embodiment in which the body 10″ has a cavity 26which is filled with spongeous bone 28. The cavity 26 extendssubstantially from the end of the reception openings 20, 22 up to andinto the region of the recesses 24. In this connection, the cavity 26 ismatched to the outer contour of the body 10″.

1. A spinal column implant for intercorporal fusion at the spinal columncomprising a body (10, 10′, 10″) of bone material having a first end andan opposing second end, the body having a substantially trapezoidalcross-section and which is made curved in the direction of itslongitudinal extension, whereby one convexly curved side (16) and oneconcavely curved side (18) is formed, and wherein the implant is matchedin size to an intervertebral space present between adjacent vertebraeafter removal of the intervertebral body, wherein a first and a secondouter side (17, 19) connecting the one convexly curved side and the oneconcavely curved side are inclined in the direction of the one concavelycurved side so as to form a cross-section tapering towards the concavelycurved side, and wherein at least one end of the body is rounded in planview into a semi-circular shape, wherein the first end has at least onereception opening for an application tool and the opposing second endhas a plurality of notches formed across a transition between theconcavely curved side and a curved surface of the second end, whichallows the taking along of loosely introduced bone powder into theintervertebral space.
 2. A spinal column implant in accordance withclaim 1 characterized in that the body (10, 10′, 10″) is formed ofpreserved and sterile bone material of human or animal origin.
 3. Aspinal column implant in accordance with claim 1, characterized in thatthe first end and the second opposing end of the body (10, 10′, 10″) arerounded in plan view in a semi-circular shape.
 4. A spinal columnimplant in accordance with claim 1, characterized in that the body(10,10′, 10″) has rounded edges.
 5. A spinal column implant inaccordance with claim 1, characterized in that the body has the form ofa ring segment.
 6. A spinal column implant in accordance with claim 1,characterized in that the second end (14) of the body (10′) is narrowerthan the first end (12).
 7. A spinal column implant in accordance withclaim 1, characterized in that the body (10, 10′, 10″) is trapezoidal incross-section having obliquely extending sides deviating from across-section in the form of a rectangle with rounded edges by an angle(α) from approximately 3° to 60°.
 8. A spinal column implant inaccordance with claim 2, wherein said preserved and sterile bonematerial is bovine bone material.
 9. A spinal column implant inaccordance with claim 5 wherein said ring segment forms one-third toone-half a complete ring.
 10. A spinal column implant in accordance withclaim 1 further comprising bone powder in the at least one notch orrecess.
 11. A spinal column implant for intercorporal fusion at thespinal column comprising a body of bone material having a first end andan opposing second end, the body having a substantially trapezoidalcross-section and which is made curved in the direction of itslongitudinal extension, whereby one convexly curved side and oneconcavely curved side is formed, and wherein the implant is matched insize to an intervertebral space present between adjacent vertebrae afterremoval of the intervertebral body, wherein a first and a second outerside connecting the one convexly curved side and the one concavelycurved side are inclined in the direction of the one concavely curvedside so as to form a cross-section tapering towards the concavely curvedside, and wherein at least one end of the body is rounded in plan viewinto a semi-circular shape, wherein the body is smooth except for holesconsisting of an application tool reception opening in the first end anda plurality of notches which are formed across a transition between theconcavely curved side and a curved surface of the second end.